Polar Modulation is related to inphase (I) and quadrature (Q) modulation in the same way that polar coordinates are related to the Cartesian coordinate system. For polar modulation, the orthogonal I and Q components of an RF signal are converted to a phasor representation comprising an amplitude component and a phase component. In this way, the combined I and Q signal may be generated with one phase change and one amplitude change, whereas separate I and Q modulation may require amplitude and phase modulation for each channel, especially for non-constant envelope modulation modes. In addition, the I and Q modulation approach may require good linearity of the power amplifier, often leading to power inefficient designs that suffer from parameter variability due to factors such as temperature. In contrast, polar modulation may allow the use of very efficient and non-linear amplifier designs for non-constant envelope modulation schemes.
In some conventional polar modulation transmitters, an input may be represented as a phase modulation (PM) signal and an amplitude modulation (AM) signal. The PM signal may be input to a direct digital frequency synthesizer (DDFS). The DDFS may utilize the PM signal to generate a sequence binary numbers, each represented by a plurality of bits, which comprise a least significant bit (LSB) and a most significant bit (MSB). Each binary number may be converted to a corresponding voltage level. Thus, the corresponding sequence of voltage levels may form a representation of an analog signal. The analog signal may be input to a power amplifier (PA) circuit.
The AM signal may be input to the PA circuit. The PA circuit may utilize the AM signal to modify the amplitude of the input analog signal. The PA circuit is typically a non-linear amplifier, for example a Class C amplifier. The amplified analog signal may then be transmitted from the conventional polar modulation transmitter.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.